Capital gains

I will assume that the houses you bought and sold were your primary residence. 

If you bought your most recent primary residence in 2021 and then sold it in 2022, you would not normally qualify to exclude the gain because you had not lived in the home long enough (two years).  Also, if you excluded the gain when you sold your residence in 2021, you would not qualify to exclude the gain on the 2022 home sale because you can only claim the exclusion once during a 2-year period.  

However, there is an exception to the 2-year requirement if your home was destroyed or your home suffered a casualty loss because of Hurricane Ian. If that exception applies, you may qualify for a partial gain exclusion on the 2022 sale.   

This link provides more information on the rules for excluding the gain on your primary residence:  https://www.irs.gov/publications/p523

For any gain that you aren't able to exclude, you'll need to report the sale on your tax return for 2022.  You don't mention whether you owned the house for more than a year, so the gain may be long term or short term, depending on whether you held it for longer than a year. 

If the gain is short term, it is taxed at the regular tax rates for ordinary income. 

If the gain is long term and you are single with taxable income under $41,675, the long term capital gain would be taxed at 0%.  If your taxable income is between $41,675 and $459,750, the long term capital gains rate is 15%.  If you are married, your income must be under $83,350 for the 0% rate and between $83,350 and $517,200 for the 15% rate.  

Your question asked "When and what percentage of capital gains will I have to pay if my income is under 40,000 for 2024?"  I've assumed that the 2024 is a typo and you meant 2022, since you sold the home in 2022.